NEAR MADAYA, Syria/BEIRUT/GENEVA Aid was sent on Thursday to a Syrian town blockaded by pro-government forces and two villages besieged by rebels for the second time this week, and a U.N. official said he hoped to make more deliveries to areas where people are starving.

Dozens of trucks left Damascus for the town of Madaya at the Lebanese border, and the two villages of Kefraya and al-Foua in rebel-held Idlib province. Tens of thousands of people have been trapped in the areas for months.

A senior U.N. official accompanying the convoy said he hoped for smooth operation, though bad weather may delay the delivery to Kefraya and al-Foua. "We hope that with the facilitation and the agreement between the parties to this agreement that this effort will continue," Yacoub El Hillo, the U.N. resident and humanitarian coordinator in Syria, said.

A second U.N. official said starving civilians to death was a war crime whose perpetrators should be prosecuted.

"We condemn any such act, starving civilians is a war crime under international humanitarian law and of course any such act deserves to be condemned, whether it’s in Madaya or Idlib," said U.N. Human Rights High Commissioner Zeid bin Ra’ad.

"Should there be prosecutions? Of course. At the very least there should be accountability for these crimes."

The siege of Madaya, where people have reportedly died of starvation, has become a focal issue for Syrian opposition groups who want all such blockades lifted before they enter negotiations with the government planned for Jan. 25.

A prominent member of the political opposition to President Bashar al-Assad told Reuters that date was unrealistic, reiterating opposition demands for the lifting of sieges, a ceasefire and a release of detainees before negotiations.

"I personally do not think Jan. 25 is a realistic date for when it will be possible to remove all obstacles facing the negotiations," George Sabra told Reuters by telephone.

A total of 45 trucks carrying food and medical supplies are due to be delivered to Madaya, and 18 to al-Foua and Kefraya on Thursday, aid officials said.

The British-based Syrian Observatory for Human Rights said it had recorded 27 deaths in Madaya from malnutrition and a lack of medical supplies, and at least 13 deaths in al-Foua and Kefraya due to a lack of medical supplies.

The population of Madaya is estimated at 40,000, while about 20,000 live in al-Foua and Kefraya.

The World Food Programme said it would deliver 120 tonnes of wheat flour to Madaya, and 60 tonnes to al-Foua and Kefraya. A U.N. official said the convoy also included medical supplies, blankets, and clothing. The World Health Organization is awaiting an answer from the government to a request to send medics and mobile clinics, its representative in Damascus said.

"The scenes we witnessed in Madaya were truly heartbreaking," said Marianne Gasser, the most senior official with the International Committee of the Red Cross in Syria.

"The conditions are some of the worst that I have witnessed in my five years in the country. This cannot go on," she said.

PEACE TALKS PLANNED AS WAR RAGES

The talks planned for Jan. 25 in Geneva are part of a peace process endorsed by the U.N. Security Council last month in a rare display of international agreement on Syria, where the war has killed 250,000 people.

U.N. Special Envoy for Syria Staffan de Mistura said after meeting representatives of the United States, Russia and other powers on Wednesday that talks were still planned for Jan. 25.

But even with the backing of the United States and Russia, which support opposite sides in the conflict, the peace process faces formidable obstacles.

"The meeting is due in a bit more than 10 days, but before then de Mistura will present in New York what he has achieved," said a senior western diplomat.

"But he still has to define how to press ahead with this mechanism which to me is not looking good because all sides are not agreed on the parameters."

Fighting is raging between government forces backed by the Russian air force and Iranian forces on one hand, and rebels including groups that have received military support from states including Saudi Arabia and the United States.

Rebel groups that back the idea of a political settlement issued a statement on Wednesday rejecting any negotiations before goodwill measures from Damascus including a ceasefire.

Sabra, the opposition politician, said: "There are still towns under siege. There are still Russian attacks on villages, schools and hospitals. There is no sign of goodwill."

There are about 15 siege locations in Syria, where 450,000 people are trapped, the United Nations says.

The Syrian government has said it is ready to take part in the talks, but wants to see who is on the opposition negotiating team and a list of armed groups that will be classified as terrorists as part of the peace process.

Underscoring the complications on that issue, a senior Russian official condemned as terrorists two rebel groups that are represented in a newly-formed opposition council tasked with overseeing the negotiations.

"We do not see Ahrar al-Sham or Jaysh al-Islam as part of the opposition delegation because they are terrorist organisations. We believe that the opposition delegation should be represented not by terrorist representatives," the RIA news agency quoted Deputy Foreign Minister Gennady Gatilov as saying.

Moscow also criticised France for accusing Russia of carrying out strikes on civilians in Syria.